1. Field of the Invention
The present invention relates to a method of manufacturing a dielectric filter, particularly to a method of manufacturing a dielectric filter which is provided with a conductive layer sectioned by an insulating region on a surface of a porcelain element body.
2. Description of the Related Art
A dielectric filter is constituted, for example, by making a resonant hole in a porcelain element body formed of a dielectric material. On a surface (inner surface) of the resonant hole or an outer surface of the porcelain element body provided is a conductive layer which is sectioned by an insulating region. As manufacture methods, a screen printing technique for forming a conductive layer by using a silver paste and an electroless plating technique with copper for forming the conductive layer are known.
In the screen printing technique, each face of the porcelain element body needs to be printed and dried. Since a large number of processes are required for repeating printing and drying, a period of time for the manufacture is disadvantageously prolonged. Also in the screen printing, the enhancement of pattern precision is restricted. In a subsequent process, the conductive layer required to be trimmed, which deteriorates the productivity.
In the electroless plating technique, a masking material of resin or the like is applied beforehand to the insulating region where an insulated state should be kept. Subsequently, a catalyzer application process is performed in such a manner that no catalyzer layer is formed on the insulating region. Then, a plating process is performed.
However, even when the masking material is used, a conductive metal is deposited on the masked region in many cases. As a result, insulation defects are caused. Therefore, after the plating process a process for removing an excessively deposited plating is necessary. Hence, product quality is deteriorated, and only a poor productivity is provided.
To solve the problem with the electroless plating technique, a manufacture method disclosed in the Japanese Patent Application Laid-open No. Hei 6-334414, partially removes a surface plating layer with an ultrasonic cutter to form an insulating region.
In the method, the plating layer is removed by an ultrasonic cutter to form the insulating region. The, the ultrasonic cutter is required to remove a hard and thick plating layer of e.g., copper with a thickness of, e.g., 2 to 10 .mu.m. Therefore, when the insulating region is formed, a period of time of one second or more is necessary for removing the plating layer, which fails to improve productivity.
Also, in the conventional method in which the hard and thick plating layer is removed, the ultrasonic cutter is required to provide power of 50 W or more. During such a process machining accuracy is lowered, and the cutting tool is easily damaged. Therefore, a cost for replacing the cutting tool disadvantageously contributes to the increase of cost for manufacturing dielectric filters.